1. Field of the Invention
This invention relates to a magnetic recording disc jacket, and more particularly to a jacket for retaining therein a magnetic recording disc while the recording disc is in use in a magnetic disc recording and reproducing machine.
2. Description of the Prior Art
A magnetic recording disc jacket is, as disclosed in U.S. Pat. No. 3,668,658 and Sidney Davis, Computer Design, Pages 55 to 64 (June 1973) Published by Computer Design Publishing Corp., Amsterdam, Netherland, made of plastic sheet material which rotatably retains therein a magnetic recording disc (hereinafter referred to simply as a "disc"). The disc has a thickness of 80 .mu.m and a diameter of 20 cm, and the disc jacket has a thickness of 2 mm and is 20.3 cm square. The disc jacket is used for not only retaining the disc but also for holding the same while the disc is driven in a magnetic disc recording and reproducing machine (hereinafter referred to as a "magnetic disc recorder" or simply as a "recorder").
The conventional disc jacket is provided on the inner surface thereof with a fibrous layer made of nonwoven cloth or the like for protecting and cleaning the surface of the disc. In order to reduce the torque required for rotating the disc retained in the disc jacket, it is known to use a lubricant on the inner surface of the disc jacket. For example, it is disclosed in German Pat. No. 2,545,091 that the nonwoven cloth can be impregnated with a lubricant mainly consisting of fluoridized alkylpolyether so that the disc may be smoothly rotated in the disc jacket.
However, the torque required for rotating the disc in a disc jacket is also increased by an electrostatic force induced between the disc and the fibrous layer. The electrostatic force is created by the electrostatic charges carried by the disc. The disc is electrostatically charged by the friction between the disc and the fibrous layer on the inner surface of the disc jacket.
The increase in torque prevents the smooth rotation of the disc and this results in drop-outs of the recording and reproducing signals. Further, by the friction between the fibrous layer and the disc, the fibers of the fibrous layer are apt to be abraded. Furthermore, the electrostatic charges carried by the disc surface attract dust, magnetic material chips and fiber chips, which results in signal drop-outs.